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Air Masses, Fronts and Storms Pages 670-673 Air Mass An _________ ___________ is a large body of air that sits over an area a long time. It sits there long enough to take on the _____________________ of the area. The names are a combination of letters that tell ____________________ they formed 1st over land or sea continental © maritme (m) nd 2 approximate latitude artic (a) polar (p) tropical (t) General Characteristics Maritime will be ___________________ Continental _________________________ Maritime and tropical are abbreviated with __________________letters Arctic will be ______________ Polar _____________ ________________ as cold Tropical ______________________ Continental Polar (cP) Source Formed over continent Near poles Characteristics Cold Dry Surface type lowercase letter m maritime c continental Source region is uppercase A arctic P polar T tropical What will the characteristics of these air masses be? 8 points mA cA cT cP Maritime Tropical (mT) ________________ Near equator and over water ________________________ Warm Moist Wrap Up Characteristics cP continental polar cold, dry, stable cT continental tropical hot, dry, stable air aloft--unstable surface air mP maritime polar cool, moist, and unstable mT maritime tropical warm, moist, usually unstable Continental polar and continental arctic produce cold _______________ winters Maritime polar and maritime arctic pick up moisture and bring cool _________weather Fronts Fronts form where air masses ________________ They are named for the ___________________ Cold front ______________ air invades warm air Warm front ______________ air invades cold air When the two masses meet, the differences in temperature, moisture and pressure can cause one air mass to ________________________ the other. Other fronts If neither air mass is moving a _______________________ front If a cold front ________________ a warm front it is an occluded front We find a variety of weather at fronts Fronts are accompanied by _____________, __________, __________ and ________________. Approaching warm front Less dense air gradually rises over the cold denser air Less obvious and more gradual than cold front Cirrus clouds Thicken into altocumulus and altostratus Sky turns gray Light to moderate rain or snow develops At front rain or snow turns to drizzle I. Atmospheric Lifting For clouds to form air must ___________________________ 3 lifting mechanisms 1. 2. 3. I. Convectional Lifting Some areas of Earth's surface pick up heat better than others. As air warm it becomes less _______________ and rises. As it rises it cools and sinks Circulatory motion is called convectional lifting If cooling occurs close to the air's saturation temperature, condensing moisture forms a cumulus cloud Form and dissipate over the same area II. Orographic Lifting An air mass is lifted when it is pushed _________________over an obstacle such as a _______________________ range As rising air cools______________ stratus If unstable air cumulus As air moves down the other slope it warms The Name of the Wind is _____________________ The descending air is dry because the moisture was removed on the other side. This is called the _____________ __________________ _______________. Example: Eastern Colorado and western Kansas See figure 27.10 III. Frontal Lifting When fronts collide warm less ______________ air is ________________up over cold dense air Thunderstorm Formation As cold air pushes into warm moist air, the cold more dense air stays low and the warmer less dense air is pushed up _______________ This rapid upward movement forms _______________________ Fronts—dryline The source region for cT air is the desert Southwest, the high plains and Mexico with relation to the United States. The air has low dewpoints and warm to hot afternoon temperatures but with mild nighttime temperature. Skies are generally clear in cT air. This allows daytime heating during the day and radiational cooling at night. The cT air mass is most prevalent in summer; in the cool season it is not as discernible. Due to the buoyancy and elevation of cT air across North America, this air will advect into the mid-levels of the atmosphere once it moves out of its source region. This creates a cap of mild dry air. If this air advects over PBL mT air, the severe thunderstorm threat increases significantly. The boundary of cT is most noticeable with the creation of a dryline. A dryline separates mT air from cT air. Depending on the strength of the dryline, convergence along the dryline and the dynamics above the dryline, severe thunderstorms can form near a dryline boundary. Hail Formation Hail stones form by ____________________ Small hail gets caught up in the updraft and goes to the top of the cloud where it receives another _________________ of ice This repeats until the hail cannot be _______________________ by the _______________ and it falls Hail requires strong _____________________ to form For the smallest hail to form, an updraft of around 36 to 54 km/h (24-34 mph) is required. golf-ball size (1 3/4 inch diameter) -- require updrafts of around 88 km/h (55 mph) to form. Softball-size hail involves updrafts exceeding 160 km/h (100 mph). Record Hail Record hail fell in Coffeyville, KS diameter 14.4 cm (5.67 inches)